Selection of content from a stream of video or audio data

ABSTRACT

A main stream contains successive content elements of video and/or audio information that encode video and/or audio information at a first data rate. A computation circuit ( 144 ) computes main fingerprints from the successive content elements. A reference stream is received having a second data rate lower than the first data rate. The reference stream defines a sequence of the reference fingerprints. A comparator unit ( 144 ) compares the main fingerprints with the reference fingerprints. The main stream is monitored for the presence of inserted content elements between original content elements, where the original content elements have main fingerprints that match successive reference fingerprints and the inserted content elements have main fingerprints that do not match reference fingerprints. Rendering of inserted content elements to be skipped. In an embodiment when more than one content element matches only one is rendered. In another embodiment matching is used to control zapping to or from the main stream. In another embodiment matching is used to control linking of separately received mark-up information such as subtitles to points in the main stream.

The invention relates to a method and apparatus for selection of contentfrom a stream of data, in particular video and/or audio data, that hasbeen distributed for example by means of broadcasting. Moreparticularly, according to one aspect, the invention relates to a methodand apparatus for replay of a stream of data, in particular video and/oraudio data, that has been edited after it has been distributed.According to one aspect, the invention relates to a method and apparatusfor channel switching (zapping).

Television broadcasts typically contain successive items of content.Examples of items of content are motion pictures, sports gameregistrations, talk shows etc. Video recording equipment has beendesigned to record and replay selected items from such broadcasts,typically by means of selection under control of a timer. A well-knownproblem of timer controlled recording is that does not take account ofunpredicted delays of the broadcast of an item, unpredicted extension ofthe item etc. Moreover, timer controlled recording inevitably alsorecords commercials that have been inserted in the stream, andrepetitions of brief preceding parts of the selected item immediatelyafter commercials.

A number of improvements over timer based recording and replay have beensuggested in the prior art. US patent application No 20010051037, forexample, discloses how automated access to an electronic program guidecan be used to enable a recorder to select the start and end times of arecording more accurately. When the electronic program guide is updatedwith information about broadcast delays and time extensions of a contentitem, the recorder that is programmed to record the item can adapt thestart and end times accordingly. An electronic program guide is anexample of the use of an index table for a broadcast stream withpointers to time points in the stream where the content changes.

Another solution proposed by US patent application No 20010051037 is theuse of mark up tags in the broadcast stream itself, from which therecorder can determine the start and end of an item of content. USpatent application No. 20020176702 similarly uses the use of identifiersin the broadcast stream, which can also be used to eliminate recordingof commercials.

These solutions have the problem that the broadcaster must provideadditional information that is dedicated to abnormal access to thestream, in the form of an index table (e.g. a real-time updatedelectronic program guide) or mark up tags. Errors in this additionalinformation, as well as failure to provide proper timing, cansignificantly affect recording. Moreover, the broadcaster may bereluctant to provide this information because it is merely overhead, orbecause it only reduces attractiveness of the television channel foradvertisers. The same kinds of problems occur when the data isdistributed for example on disk.

In addition to recording and replay additional information may have usefor other applications, such as automated intelligent zapping or mark upof video information. An apparatus that supports automated intelligentzapping may for example be designed to skip channels that arebroadcasting commercials or to zap back to an original channel oncebroadcast of an original item of video information is resumed on thatchannel. For this purpose the same type of information is needed as forselective recording, suffering from the same problems if thatinformation is not accurate.

Mark up of video information may involve adding subtitles, alternativelanguage audio information, chapter markers, menu's, premium contentetc. For this purpose the same type of information is needed as forselective recording, suffering from the same problems if the informationis inaccurate.

From PCT patent application No 2004019527 (assigned to the same assigneeas the present patent application) it is known to trigger a videorecorder by means of digital fingerprint matching (the fingerprintsbeing called “signatures” in this publication). PCT patent applicationNo 2004019527 gives examples of fingerprint computation techniques. Asused herein, “fingerprint” refers to information that is obtained from asignal (or signal part) that represents video and/or audio content, sothat the fingerprint is substantially affected by factors that determinethe perceptive impression when a human viewer and/or listener when thevideo and/or audio content perceives content. Thus, the fingerprint isto a large extent unique for the perceived content. In this sense afingerprint as used herein differs from a watermark in video and/oraudio signals in that a watermark is independent on the perceptivecontent.

The recording method of PCT patent application No 2004019527 is based onthe observation that content items on television often start with thesame introductory images, called the “intro”. A fingerprint of anexample of the intro is computed and fingerprints of an incoming videostream are computed and compared with the fingerprint of the intro. Whena match is found the recorder is started.

PCT patent application No 2004019527 describes use of fingerprint tosearch for intros in recorded material, to facilitate selective replay.However these known fingerprint method are limited to content that ispreceded by a known intro. Selection of content is limited to the pointat the start of programs which contains standard imagery.

Among others it is an object of the invention to enable fine grainedselection of insertions in a video and/or audio stream after the streamhas been distributed with the insertions, preferably from a broadcaststream, without requiring a table of addresses in the stream from thedistributor or mark up tags in the stream.

Among others it is an object of the invention to enable substantiallyseamless reconstruction of an item of video and/or audio informationthat is distributed in a video and/or audio stream intermixed with othervideo and/or audio data.

Among others it is an object of the invention to enable intelligentzapping among a plurality of video and/or audio streams that arebroadcast simultaneously, without requiring a table of addresses in thestream from the distributor or mark up tags in the stream.

Among others it is an object of the invention to support mark-up ofvideo and/or audio streams that is broadcast.

An apparatus and method according to the invention are set forth in theindependent Claims. According to the invention fine grained matching offingerprints (in the sense defined in the preceding) for a main streamof video and/or audio data is made possible by the supply of anadditional reference stream which defines a series of fingerprints and asequence order of these fingerprints. The reference stream may bedistributed in the form of a file, for example. The reference streamcorresponds to a core of the main stream (e.g. a motion picture), butnot to inserted sections in the main stream (e.g. commercials) that donot correspond to the core of the main stream. The reference streamusually has a lower data rate than the main stream. That is, the amountof data used for corresponding rendering time intervals is lower in thereference stream than in the main stream. In one embodiment, thereference stream is a low (temporal or spatial) resolution version ofthe main stream without commercials. In this case reference fingerprintscan be computed from the video and/or audio content of the referencestream and their sequence can be derived from the sequence of thereference stream. In another embodiment the reference stream containsthe reference fingerprints directly.

The supply of this type of reference stream makes it possible to editthe main stream. Since the reference stream may have a much lower datarate than the main stream, the reference stream can be “sold” to enableimproved quality access to the main stream without the need toredistribute a stream at the high data rate of the main stream.Preferably the fingerprints of the main stream and the reference streamare matched according to their respective positions in the main streamand the reference stream. That is, a main fingerprint obtained for aparticular content element from the main stream is detected to match ifit substantially equals a particular reference fingerprint obtained fromthe reference stream and a main fingerprint for a further contentelement from the main stream that is temporally adjacent to theparticular content element also matches.

In an embodiment the reference stream is also used to detect duplicationof content in the main stream, such as for example just in front andafter an inserted commercial. In this way it can be ensured that onlyone copy of the duplicated part is rendered. In principle duplicationcan be detected simply by testing whether the same reference fingerprintmatches with the fingerprint of more than one content element of themain stream. In a preferred embodiment duplication of a stream sectionis eliminated provided that it is detected that the section immediatelyprecedes and follow a same section of inserted content elements (asdetected by the absence of a matching fingerprint). Thus, the risk ofaccidental elimination of duplication is avoided.

Another application is that the reference stream may be used to supportintelligent zapping, for example by skipping channels that broadcastinformation with fingerprints that do not match reference fingerprints,or by returning to a main channel, terminating zapping once matchingfingerprints are found in the video and/or audio data of the mainchannel.

Another application is that the reference stream may be used to add markup information. The mark up information, such as sub-title information,alternative language channels, menus, chapter markers, premium contentetc. may be supplied in conjunction with the reference stream, so thatthe mark-up can be linked to positions in the reference stream that areselected by fingerprint matching. In this way a high quality stream canbe constructed for individual users, without requiring the fullbandwidth for transmission of the stream to be reserved for theseindividual users (this bandwidth is provided in a broadcast channel thatis shared with other users that do not receive the mark up information).

These and other objects and advantageous aspects of the invention willbe described in more detail using non-limitative examples illustrated bythe accompanying Figures.

FIG. 1 shows a video and/or audio rendering system

FIG. 2 symbolically shows a broadcast stream of video and/or audio data

FIG. 3 symbolically shows a reference stream of video and/or audio data

FIG. 3 a symbolically shows associations between time points

FIG. 4 symbolically shows an edited stream of video and/or audio data

FIG. 5 shows a video and/or audio rendering system with automatedzapping

FIG. 6 shows a video and/or audio rendering system that supports mark-up

FIG. 1 shows a video and/or audio rendering system comprising abroadcast transmission apparatus 10, a reference transmission apparatus12 and a receiver apparatus 14. Receiver apparatus 14 comprises achannel receiver 140, a storage device 142, a reference comparator 144,an editing unit 146 and a rendering unit 148. Channel receiver 140 hasan input for receiving a broadcast data stream from broadcasttransmission apparatus 10 and an output coupled to storage device 142.Editing unit 146 has an interface coupled to storage device 142 and anoutput coupled to rendering unit 148. Rendering unit 148 comprises forexample a display screen and/or a loudspeaker for rendering video and/oraudio information supplied by editing unit 146. Reference comparator 144has an input 141 for receiving a reference stream from referencetransmission apparatus 12, an interface to storage device 142 and anoutput coupled to a control input of editing unit 146.

In operation broadcast transmission apparatus 10 broadcasts a stream ofvideo and/or audio data and reference transmission apparatus 12transmits a reference stream. FIG. 2 illustrates a broadcast stream 20as a function of time T. The stream contains an item of videoinformation, such as a motion picture, which has been cut into parts 22a-g that are broadcast temporally intermixed with other items 24 a-fsuch as commercials. Ordinarily, when stream 20 is received, decoded andrendered, this would result in visual and/or acoustical rendering of theparts 22 a-g intermixed with visual and/or acoustical rendering of theother items 24 a-f.

FIG. 3 illustrates a reference stream 30. The reference stream 30 iscontains parts 32 a-g that correspond to a transmits a reference signal.In contrast to the broadcast stream 20 the parts 32 a-g are notintermixed with other items. In an embodiment, reference signal 30contains a series of fingerprint data items, each corresponding to afingerprint that can be computed from the video and/or audio data of arespective section of the broadcast stream 20, e.g. from video data inrespective video frames, or groups of frames or time intervals of audio.In an alternative embodiment, reference stream 30 contains elements thatrepresent the audio and/or video-encoding elements from the broadcaststream at low spatial and/or temporal resolution, without intermixedcommercials. In each embodiment the information in the reference streamis constructed so that the data rate (and thereby the number of databits that needs to be transmitted for a same time interval duringrendering) in reference stream 30 is much lower than the data rate inbroadcast stream 20. This indicated symbolically by the fact that thebroadcast stream 20 of FIG. 2 is drawn with broader than the referencestream 30 of FIG. 2.

In operation, receiver apparatus 14 receives both broadcast stream 20and reference stream 30. In principle the same communication medium maybe used to receive both streams (e.g. from satellite or terrestrialwireless broadcast, or from a cable TV network). However, preferablydifferent media are used, reference stream 30 being received via theInternet for example, or distributed on a data carrier like a disk.Channel receiver 140 receives the broadcast stream and stores data fromthat stream in storage device 142 which may contain a magnetic harddisk, a flash memory etc.

After the broadcast stream of a part of it has been stored editing unit146 starts retrieving data from the stream from storage device 142,decodes the retrieved data to derive a video and/or audio signal andsupplies the decoded signal to rendering unit 148. Editing unit 146 isarranged to skip selected parts of the broadcast stream 20, so thatrendering unit 148 does not render the corresponding video and/or audiosignal for those parts. Reference comparator 144 controls the selectionof the parts that are skipped. Reference comparator is implemented forexample as a suitably programmed programmable processor, or as adedicated circuit.

Reference comparator 144 receives reference stream 30. In an embodimentreference stream 30 is received substantially simultaneously withbroadcast stream 20, but alternatively reference stream 30 may bereceived earlier or later. Preferably reference comparator 144 storesthe entire reference stream 30, or parts of it, or fingerprints computedfrom reference stream 30, for later use, for example in storage device142 or in another memory. Alternatively reference comparator 144 mayreceive reference stream 30 for substantially immediate use, in whichcase no long-term storage of the entire reference stream 30 is needed.

During editing reference comparator 144 retrieves sections of broadcaststream 20 from storage device 142, computes fingerprints for thoseretrieved sections and compares these computed fingerprints withfingerprints obtained from reference stream 30. Example of fingerprintcomputation techniques can be found in WO2004019527. When referencestream 30 contains a series of fingerprints these fingerprints may becompared substantially directly with the computed fingerprints, but inan embodiment wherein reference stream 30 contains a low resolutionversion of the elements of broadcast stream 20, but no fingerprints, thefingerprints may need to be computed from the low resolution versionfirst, before comparison.

As a result of comparison reference comparator 144 detects for whichsegment of broadcast stream 20 the fingerprint matches a particularfingerprint obtained from reference stream 30. In this case a time pointdefined by reference stream 30 is associated with the segment ofbroadcast stream 20 that resulted in the matching fingerprint.

FIG. 3 a uses connecting lines to symbolize the resulting association oftime points defined by reference stream 30 with time points in broadcaststream 20 (typically a time points in broadcast stream 20 defines thestart of a segment from which a matching fingerprint was computed or forexample a video frame from which a matching fingerprint was computed).It should be understood that only a few of the associations areillustrated for the sake of clarity. Typically, there associations aredetected for time points that are no more than one second apart andpreferably no more than a tenth of a second apart. At one point it isshown that two time points separated by a commercial break in broadcaststream 20 are associated with one time point defined by reference stream30. This may occur under special circumstances as will be discussedlater.

The time points that have been detected to be associated in this waywith broadcast stream 20 are used to control editing by editing unit146. Typically it will be found that during parts 22 a-g successivesegments of broadcast stream 20 are associated with successive timepoints. For interruptions 24 a-f no matching fingerprints will be foundand a next time point will only be associated with a next part 22 a-g ofbroadcast stream 20 after the interruption 24 a-f. In an embodimentediting unit 146 selectively skips segments of the broadcast stream 20that are not associated with time points defined by reference stream 30.In a further embodiment fingerprints are determined for sampled segmentsthat are separated by other segments for which no fingerprint matchingis performed. In this embodiment the other segments from broadcaststream 20 between segments for which matching segments were found notskipped. Other segments from broadcast stream 20 between segments forwhich no matching segments were found are skipped. Preferably, editingunit 146 selects the length of the skipped parts so that the remainingparts of the broadcast stream 20 will be rendered at mutual distancesdefined by the associate time points.

In many broadcast streams 20 in which an item of video and/or audio datais interrupted by commercials a last part of the item that precedes thecommercial is repeated after the commercial. This is done to allow theviewer to regain the context after the commercial, before new videoand/or audio information is rendered. In this case, it may occur thatreference comparator 144 identifies two segments from broadcast stream20 whose fingerprints match the same fingerprint obtained from referencestream 30. Preferably, it is also detected whether these duplicatesegments immediately precede and follow the same inserted segmentrespectively. Editing unit 146 is preferably arranged to skip one ofthese two segments, in response to detection of such a duplication, sothat the remaining parts of the broadcast stream 20 will be rendered atmutual distances defined by the associate time points.

In an embodiment, editing unit 146 includes all segments from broadcaststream 20 up to a first segment of which the fingerprint did not match afingerprint obtained from reference stream 30 (at the start of acommercial break 24 a-f). In this case the fingerprints obtained fromreference stream 30 include a sequentially first subsequent fingerprintthat does not match with a fingerprint computed from broadcast stream 20for a segment at a normal time distance from a previous segment ofbroadcast stream 20 for which a matching fingerprint was obtained fromreference stream. Reference comparator 144 searches for a subsequentsegment in broadcast stream 20 (after the commercial break 24 a-f) witha fingerprint that matches the sequentially first subsequentfingerprint. This corresponds to the first as yet unbroadcastinformation after the commercial break. Editing unit 146 skips broadcaststream 20 until this subsequent segment. In this way the commercialbreak and the duplicated part of the stream is eliminated.

It will be appreciated that other solutions are possible, such asskipping a last part of broadcast stream 20 before the commercial breakand resuming immediately behind the commercial break from the firstsegment with a matching fingerprint. Other solutions may be used whichskip part of the broadcast stream before and part after the commercialbreak as long as a substantially continuous flow of time points isrealized.

FIG. 4 illustrates composition of the output stream 40 that is suppliedto rendering unit 148. Relative timing of the start of parts 22 a-g ofthe item from broadcast stream is controlled by time points defined byreference stream 30 for matching fingerprints, and repetitions areprevented by starting successive parts 22 a-g before preceding partshave been completed.

It will be appreciated that this technique is not limited to eliminationof repetitions around commercial breaks. Other repetitions, for examplereplays during sports games may be used as well. In this case a searchis made for duplicate fingerprint matches and editing unit 146 skipsbroadcast stream 20 from a first segment whose fingerprint matches asame fingerprint from reference stream 30 as a preceding segment frombroadcast stream 20, to a first next first segment from broadcast stream20 whose fingerprint matches a fingerprint from reference stream 30 thatdoes a preceding segment from broadcast stream 20. Preferably, editingunit 146 is switchable between respective modes in which this type ofskipping is enabled and disabled respectively. Preferably editing unit146 is also arranged to prevent skipping if the length of time intervalthat is to be skipped exceeds a threshold length.

Any type of search for segments with matching fingerprints may be used.In an embodiment reference comparator 144 selects an initial position ofa next segment from broadcast stream 20 for which a next fingerprint ismatched to a particular fingerprint from reference stream 20 by anoffset from a preceding segment with a fingerprint that matches apreceding fingerprint from the reference stream. The offset is selectedequal to the time interval defined by the reference stream between thepreceding fingerprint and the next fingerprint. If no match is found atthe initial position new comparisons are performed for successivesegments of the broadcast stream 20, until a segment is found thatmatches the next fingerprint from the reference stream 30. This has theadvantage that no search will be performed for further fingerprints fromthe broadcast stream 20 that match a particular reference fingerprint,once a fingerprint for the broadcast stream has been found that matchesthe reference fingerprint. Thus, the risk of accidental matches isreduced.

An exception is preferably made however, if it is detected that the mainfingerprint from the broadcast stream that matches the particularreference fingerprint is followed in the broadcast stream by a mainfingerprint that does not match. In this case a search made forsubsequent duplicate matches of the particular reference fingerprintwith main fingerprints from the broadcast stream. In this wayduplication of content before and after interruptions can be detected.

However, it should be understood that alternatively a search formatching fingerprints may be conducted by comparison of a fingerprintsfrom reference stream 30 with a plurality of fingerprints for a rangetime points from broadcast stream 20, or vice versa by comparing afingerprint from broadcast stream 20 with a plurality of fingerprintsfor a range time points from reference stream 30. This works well whenthe fingerprints are sufficiently unique.

In an embodiment the comparison of the fingerprints, and optionally thecomputation of the fingerprints is performed during rendering, while thebroadcast stream 20 is read from storage device 142. For this embodimentthe reference stream 30 may be supplied at a different time thanbroadcast stream 20, for example only during rendering. This has theadvantage that edited rendering can be selectively enabled by latersupply of reference stream 30, e.g. after payment of a fee, or after alapse of time (e.g. for non-live viewing of a game of sports).

It should be understood that other embodiments are possible. Forexample, reference comparator 144 may be arranged to computefingerprints and select matching time points in reference stream 30 andbroadcast stream 20 in advance. In an embodiment reference comparator144 stores information about the matching time points in an index tablefor use by editing unit 146 during rendering. These computations may beperformed when the broadcast stream 20 is recorded or while thebroadcast stream 20 is present in storage device 142.

In another embodiment the described editing on the basis of fingerprintsis performed already during reception and storage of the broadcaststream 20. This reduces the amount of data that needs to be retained instorage device 142. Alternatively, editing may be performed afterstorage, but before rendering, by selectively deleting parts of thestored broadcast stream 20 from storage device 142.

Although these embodiments have been described for a broadcast stream20, which has been broadcast by a broadcast transmission apparatus 10,e.g. via a terrestrial broadcast medium, or via cable or satellitebroadcast, it should be understood that the described techniques can beapplied to a stream that is distributed via other media, for example onan optical disk like a DVD etc. In this way the value of the distributedstream can be upgraded by supplying a reference stream, withoutconsuming the bandwidth for a full data rate stream. Moreover, theinvention is not limited to applications wherein the stream isnecessarily stored.

FIG. 5 shows a system wherein the invention is applied to intelligentzapping. In this embodiment a reception apparatus 50 with a remotecontrol unit 52 is used. Reception apparatus 50 contains a secondchannel receiver 54 and a channel selector 56. Like channel receiver140, which will be referred to as first channel receiver 140, secondchannel receiver 54 is coupled to receive broadcast data. Second channelreceiver 54 has an output coupled to reference comparator 144, which hasan output coupled to channel selector 56. First channel receiver 140 hasan output coupled to a decoder 58, which has an output coupled torendering unit 148. Channel selector 56 has a control output coupled tofirst channel receiver 140. First and second channel receiver 140, 54support tuning to different channels (or selection of different programsfrom a transport stream).

In operation channel selector 56 supports zapping (channel changing)under control of remote control unit 52. According to an aspect of theinvention zapping is controlled dependent on the results of fingerprintmatching. In one embodiment, channel selector 56 is arranged to controlfirst channel receiver 140 to receive successive channels selected withremote control unit 52 (e.g. by pushing a channel up or down button), topredict a next channel that will be selected and to control secondchannel receiver 54 to receive the predicted next channel.

Reference comparator 144 then compares fingerprints computed from thebroadcast stream in the predicted channel with fingerprints from areference stream for that broadcast stream and signals to channelselector 56 whether a match is found. Upon receiving a command fromremote control unit 52 to select the next channel, channel selector 56controls first channel receiver to switch to this channel if referencecomparator 144 indicates the recent presence (within a predeterminedpreceding time interval) of matching fingerprints. If no suchfingerprints have been found channel selector 56 controls first channelreceiver 140 to switch to another channel in response to the command. Inthis way zapping automatically skips a channel that does not match areference stream.

In a further embodiment, channel selector 56 is arranged to respond tothe absence of matching fingerprints in the predicted next channel bypredicting a predicted subsequent next channel that will be selectedduring zapping after the predicted next channel and to cause secondchannel receiver 54 to receive the predicted subsequent next channel.Reference comparator 144 then compares fingerprints computed from thebroadcast stream for the predicted subsequent next channel withfingerprints from a reference stream for that broadcast stream andsignals to channel selector 56 whether a match is found.

This may be repeated for further predicted channels as long as nomatching fingerprints are found. In this way channel selector 56 maycause more than one channel to be skipped during zapping so that therendered channel skips to the next channels for which on referencestream is available or a reference stream is available and the recentbroadcast stream contains matching fingerprints. Thus, for example, ifthe reference streams describe transmitted items but not commercials inthose items, channel selector can cause channels that are broadcastingcommercials to be skipped during zapping.

Other applications are possible. For example, in another embodimentchannel selector 56 may be used to allow zapping during the time that acommercial is broadcast on a preferred channel and to switch back to thepreferred channel at the end of the commercial. For this purposeembodiment channel selector 56 may be arranged to set second channelreceiver 54 to a selected channel during zapping of the channelselection of first channel receiver 140 and to disable zapping andswitch back channel receiver 140 to the preferred channel once amatching fingerprint is detected in the broadcast stream from thepreferred channel. In a further embodiment channel selector 56 isarranged to support different zapping modes, wherein mutually differentuse is made of the fingerprint information.

FIG. 6 illustrates an embodiment wherein reference transmissionapparatus 12 also transmits mark-up information in the reference stream30. Mark-up information as such is known for example from DVD systemsand may include for example sub-title information in one or morelanguages, alternative audio channels, menus for accessing the stream,chapter markers, or premium video information that is not included inthe broadcast. Reference transmission apparatus 12 transmits informationthat links the mark-up information to video information or fingerprintsof the video information in the reference stream.

In the embodiment of FIG. 6 an information selection circuit 60 receivesthe reference stream, extracts the mark-up information and stores themark-up information in storage device 142. Reference comparator 144compares fingerprints for the broadcast stream with fingerprintsobtained from the reference stream that reference transmission apparatus12 has linked to an item of mark up information. When it detects amatch, reference comparator 144 stores information in storage device 142that links the relevant part of the broadcast information to the mark-upinformation. This may be done for example so as to construct the type ofinformation that is contained in a DVD disk (which allows language orsubtitle selection, viewing of menu's and/or chapter tables, viewing ofpremium content etc.) from a combination of data from the broadcaststream and the reference stream.

In the embodiment of FIG. 6 editing unit 146 may be arranged as a DVDreplay controller to process the stored information basically as if itwas received from a DVD disk, allowing the user to access theinformation interactively, to select languages or subtitles etc. Ofcourse, other types of access (not similar to DVD access may be used).

Although the invention has been illustrated using an embodiment using areceiving apparatus 14 with different components, it will be understoodthat in practice the different components may be implemented using thesame circuits, or using suitably programmed programmable computers toimplement any or all of the functions such as fingerprint computation,matching and editing. Accordingly the invention also encompassescomputer program products with instructions which when executed by sucha computer make the computer perform the invention.

The invention claimed is:
 1. An apparatus comprising: a comparator unitarranged to: receive a main stream and a reference stream, the mainstream having a higher data rate than the reference stream andcomprising successive content elements and inserted sections intermixedwith the successive content elements, the reference stream definingsequential reference fingerprints that correspond to the successivecontent elements of the main stream but not to the inserted sections inthe main stream; compute a main fingerprint from the successive contentelements; and compare the main fingerprint with a reference fingerprintamong the sequential reference fingerprints defined by the referencestream that has a lower data rate than the main stream; and a controlunit arranged to select content elements from the main stream based onwhether the main fingerprint matches the reference fingerprint among thesequential reference fingerprints defined by the reference stream thathas the lower data rate than the main stream.
 2. The apparatus of claim1, wherein the control unit is adapted to select the content elementsfrom the main stream if the main fingerprint mismatches the referencefingerprint and to cause a rendering of the content elements to beskipped.
 3. The apparatus of claim 1, wherein the comparator unit isarranged to detect that multiple instances of the main fingerprintmatches the reference fingerprint, the control unit being arranged tocause no more than one of the corresponding content elements to berendered in response to this detection.
 4. The apparatus of claim 1,further comprising a storage device adapted to store the main stream,the control unit being arranged to select content elements for which themain fingerprint matches the reference fingerprint for selectiveretrieval from the storage device.
 5. The apparatus of claim 1, furthercomprising a storage device adapted to store the main stream, as well asmark-up information received in the reference stream, the comparatorunit being arranged to cause linking information to be stored indicatingwhere the main fingerprint matches linking points in the referencefingerprint.
 6. The apparatus of claim 1, further comprising a channelselection unit arranged to switch to a rendering of a further streambased on the main fingerprint mismatching the reference fingerprint andto switch to a rendering of the main stream based on the mainfingerprint matching the reference fingerprint.
 7. The apparatus ofclaim 1, further comprising an input adapted to receive the main streamand the reference stream from mutually different distribution media. 8.The apparatus of claim 1, further comprising an input arranged toreceive the main stream via a broadcast channel.
 9. The apparatus ofclaim 1, further comprising a storage device adapted to record the mainstream, content elements for which the main fingerprint mismatches thereference fingerprint being discarded from retention in a storagedevice.
 10. The apparatus of claim 1, wherein the comparator unit isarranged to compute the reference fingerprint from lower resolutionversions of the content elements.
 11. A method comprising: receiving amain stream and a reference stream, the main stream having a higher datarate than the reference stream and comprising successive contentelements and inserted sections intermixed with the successive contentelements, the reference stream defining sequential referencefingerprints that correspond to the successive content elements of themain stream but not to the inserted sections in the main stream;computing a main fingerprint from the successive content elements;comparing the main fingerprint with a reference fingerprint among thesequential reference fingerprints defined by the reference stream thathas a lower data rate than the main stream; and selecting contentelements from the main stream based on whether the main fingerprintmatches the reference fingerprint anion the sequential referencefingerprints defined by the reference stream that has the lower datarate than the main stream.
 12. The method of claim 11, wherein thecontent elements are selected from the main stream if the mainfingerprint mismatches the reference fingerprint; and the method furthercomprises causing a rendering of the content elements to be skipped. 13.The method of claim 11, further comprising: detecting that multipleinstances of the main fingerprint match reference fingerprint; andcausing no more than one of the corresponding content elements to berendered in response to this detection.
 14. The method of claim 11,further comprising: storing the main stream; and selecting contentelements for which the main fingerprint matches the referencefingerprint for selective retrieval from the stored main stream.
 15. Themethod of claim 11, further comprising: storing the main stream, as wellas mark-up information received in the reference stream; and causinglinking information to be stored indicating where the main fingerprintmatches linking points in the reference fingerprint.
 16. The method ofclaim 11, further comprising: switching to a rendering of a furtherstream based on the main fingerprint mismatching the referencefingerprint; and switching to a rendering of the main stream based onthe main fingerprint matching the reference fingerprint.
 17. The methodof claim 11, wherein the receiving of the mainstream and the referencestream is from mutually different distribution media.
 18. The method ofclaim 11, wherein the receiving of the main stream is via a broadcastchannel.
 19. The method of claim 11, further comprising: recording themain stream, content elements for which the main fingerprint mismatchesthe reference fingerprint being discarded from retention in a storagedevice.
 20. A non-transitory computer readable medium comprising aprogram of instructions that, when executed by a programmable machine,causes the machine to perform operations comprising: receiving a mainstream and a reference stream, the main stream having a higher data ratethan the reference stream and comprising successive content elements andinserted sections intermixed with the successive content elements, thereference stream defining sequential reference fingerprints thatcorrespond to the successive content elements of the main stream but notto the inserted sections in the main stream; computing a mainfingerprint from the successive content elements; comparing the mainfingerprint with a reference fingerprint among the sequential referencefingerprints defined by the reference stream that has a lower data ratethan the main stream; selecting content elements from the main streambased on whether the main fingerprint matches the reference fingerprintamong the sequential reference fingerprints defined by the referencestream that has the lower data rate than the main stream.